The present invention relates to a power steering apparatus which can be mounted in any type of vehicle to decrease a steering force needing to be exerted by a driver.
Light-operated power steering apparatuses have become widespread recently. Such a conventional power steering apparatus uses electrical energy supplied from a battery. In this conventional power steering apparatus, the electrical energy causes a motor to operate an oil pump. Compressed oil from the pump is supplied to a power steering section to perform steering with a small force.
However, in this conventional power steering apparatus, a means for controlling a oil flow rate controlled by motor rotation and for preventing oil leakage becomes complicated, resulting in high cost and low reliability.
In order to eliminate the conventional drawbacks, a power steering apparatus is proposed in Japanese Patent Disclosure No. 55-47,963, wherein a steering unit is directly driven by a motor. Since the speed of the motor is high, the motor cannot follow a great change in steering direction. In particular, when quick turns of a steering wheel for slalom-like driving are required, the automatic steering apparatus cannot provide a sufficient performance.
Another conventional power steering apparatus is proposed in Japanese Patent Disclosure No. 46-33,327, wherein an electromagnetic clutch is constituted by two main driving members rotated in opposite directions and one driven member connected to a steering mechanism. The driven member is coupled to any one of the main driving members, thereby controlling the steering mechanism. However, the clutch generates large sliding noise, thereby discomforting the driver. In addition, the clutch is easily worn, so increasing maintenance operation and degrading reliability.
In a conventional power steering apparatus which does not use oil, the steering unit must be operated by an amount corresponding to a steering torque. Although steering torque detection is performed by a strain gauge, the strain gauge has low reliability and low sensitivity. Thus, the strain gauge is not suitable in the steering apparatus of a vehicle which requires high sensitivity.